1. Field of the Invention
The present invention relates generally to 3D imaging using a laser projector. Particularly, the present invention relates to a rapidly scanned laser system that accurately identifies locations on an object. More particularly, the present invention relates to a rapidly scanning laser system utilizing a three-dimensional data set projected onto contoured surfaces. Even more particularly, the present invention relates to a rapidly scanning laser system utilizing a three-dimensional data set projected onto contoured surfaces that incorporates a laser range-finding system for accurately determining the distance to the contoured surfaces.
2. Description of the Prior Art
Laser projectors are used to project images onto surfaces. They are utilized to assist in the positioning of work pieces on work surfaces. More recent systems have been designed to project three-dimensional images onto contoured surfaces rather than flat surfaces. The projected images are used as patterns for manufacturing products and to scan an image of the desired location of a ply on previously placed plies. Examples of such uses are in the manufacturing of leather products, roof trusses, airplane fuselages and the like. Laser projectors are also used for locating templates or paint masks during the painting of aircraft. A rapidly scanning laser system is a laser spot that moves from location to location with sufficient speed to appear as a continuous line.
The use of a scanned laser image to provide an indication of where to place work piece parts requires extreme accuracy in calibrating the position of the laser projector relative to the work surface. In the past, the systems have typically required the placement of several reference points fixed on or about the work surface. Typically, six reference points were required for sufficient accuracy. Reflectors or sensors have typically been placed in an approximate area where the ply will be placed. Since the points are at fixed locations relative to the work and the laser, the laser also knows where it is relative to the work. The requirement of six fixed reference points has been somewhat restricting in systems used for airplane fuselages. The plies and jobs utilized to attach the plies onto the airplane fuselage are very large. The reference points must be placed at locations where the plies will not cover the reference points. The use of the fixed points has thus been somewhat difficult to achieve. Furthermore, technicians are required to travel to the workplace and accurately place the fixed reference points.
To use a laser-pointing device in a high-accuracy, high-precision application, it must be positioned very accurately over a work piece or tool if it is to illuminate points on the work piece accurately. In one known technique called resectioning, a designator automatically determines its position and orientation relative to a tool by measuring the angles to three or more fiducial points on the tool. A designator is a device similar in concept to a laser light projector, but operating at a higher precision. It is used to sweep a laser beam over a surface to illuminate a curve. A fiducial point is an optical device whose position is accurately known in three dimensions. The tool is brought roughly into position with respect to the designator, for instance to within six inches. The designator, or other external optical devices, are used to sense the fiducial points (a minimum of four), and to measure the angles from the designator to them, not the distance from the designator to the tool. This is done to accurately orient the spatial and angular position of the designator with respect to the tool.
However, the designator cannot designate points accurately if the beam deflection angles cannot be controlled accurately. Resectioning also cannot be accurate if the galvanometers cannot accurately measure spatial angles to the fiducial points. One problem is that the components of the designator are subject to a number of sources of imprecision. These include non-linearities in the galvanometer response and the position detectors, differences in gain in op-amps driving the galvanometers, bearing run-out, tolerance in the mounting of galvanometers in the designator, twist or wobble in the galvanometer shafts, mirrors mounted slightly off axis, variations in mounting of the laser or other beam-steering elements, etc.
U.S. Pat. No. 5,400,132 (1995, Pierre Trepagnier) discloses an improved method of compensating for errors in a laser pointing device, especially in three-dimensional applications, by accurately controlling the angle that the laser beam makes in space. This is called rectification. In the method, the laser-pointing device is established in an accurate angular relationship to at least four fiducial points. The angular errors internal of the designator are determined by comparing actual galvanometer inputs, assuming no error in the established angular relationship. The actual galvanometer inputs are those that aim the laser beam at the fiducial points while recognizing the existence of the internal errors. The nominal galvanometer inputs are those that would aim the laser beam at the fiducial points assuming no internal errors in the laser pointing device. The angular errors are stored in a form for use during scanning by the laser pointing device to compensate for the internal errors in converting nominal direction numbers computed by a control to actual galvanometer inputs. A major drawback of this system is that a minimum of four fiducial points is required, but preferably six points, to properly project the image, or the distance to the points must be accurately known.
More recently, there has been disclosed a system in which reference points can be placed at initially unknown locations about a workplace. However, the laser is able to determine the specific location of the unknown locations of the reference points provided that at least one variable is fixed. U.S. Pat. No. 5,757,500 (1998, Kurt Rueb) discloses a system that utilizes two reference points which are spaced by a fixed distance. The system is able to calibrate its location in space and relative to the work piece by determining the angular location of the unknown locations for the reference points. The known distance between the two reference points is then relied upon to fix the location of all reference points in space and the location of the laser projector.
In all of the prior art devices, one variable must be fixed. In some, it is required that the distance between the laser projector and the work piece platform be known and fixed. This represents the xe2x80x9czxe2x80x9d axis in a three-dimension (x-y-z) system. Not knowing the distance between the laser projector and the work piece requires these prior art systems to triangulate a plurality, usually at least six, of known reference points to correctly projecting the laser image upon the work piece. In other systems, it is required that the distance between two reference points on the work piece platform be known and fixed.
In addition, all prior art devices require that the tool or object onto which an optical template is to be projected requires the object or tool to contain reference data marks. These reference data marks are based on ship set coordinates and are located using theodolites or laser tracker. A theodolite is extremely expensive piece of equipment, approximately $250,000. They are capable of five-decimal point accuracy in determining the coordinates of the reference marks. For painting template applications, 5-decimal point accuracy is unwarranted. Thus the cost of buying a theodolite cannot be justified.
Therefore what is needed is a 3D imaging system utilizing a three-dimensional data set projected onto contoured surfaces where the distance between the laser projector and the work piece platform does not need to be known. What is further needed is a 3D imaging system utilizing a three-dimensional data set projected onto contoured surfaces that can determine the distance between the laser projector of the system and the surface. What is still further needed is a 3D imaging system that can measure the distance between the laser projector and the surface, and use the distance value to properly project a laser template onto a work piece. What is yet further needed is a 3D imaging system that is sufficiently accurate for applications not requiring 5-decimal accuracy, is easy to use, and is relatively inexpensive.
It is an object of the present invention to provide a 3D imaging system utilizing a three-dimensional data set projected onto contoured surfaces where the distance between the laser projector and the work piece platform does not need to be known. It is a further object of the present invention to provide a 3D imaging system utilizing a three-dimensional data set projected onto contoured surfaces that can determine the distance between the laser projector of the system and the surface. It is another object of the present invention to provide a 3D imaging system that can accurately measure the distance between the laser projector and three reference sensors and use the distance value to properly project a laser template onto a work piece. It is still another object of the present invention to provide a 3D imaging system that is sufficiently accurate for applications that do not require 5-decimal point accuracy, is easy to use, and is relatively inexpensive.
The present invention achieves these and other objectives by providing a 3D imaging system that can accurately determine the three-dimensional location of a given surface without knowing the distance between the 3D imaging system and the surface of a work piece . The 3D imaging system of the present invention combines a laser projector and a laser range finder into one system head for accurately determining the distance between the laser projector and a work surface and to accurately project a laser template onto the work surface.
The 3D imaging system includes a laser light emitting component, a motorized focusing assembly for focusing the beam of the laser light at some distance from the 3D imaging system, a two-axis beam steering mechanism to rapidly direct the laser light over a defined surface area, a photo optic feedback component, a timing device, a controller module, a data storage device, an input power module, one or more output DC power modules, and an imaging system cooling subsystem. The laser light emitting component produces a visible laser light and may include a prism to optically correct astigmatism as well as one or more lenses that work as a beam collimator. The motorized focusing assembly, which receives the laser beam, has a focusing lens mounted to a linear actuator. The linear actuator is mechanically attached to a DC motor, which is controlled by a motor controller. The focusing assembly also includes travel limit sensors that are mounted at the ends of the travel of the focus assembly. The travel limit sensors as well as the motor controller are connected to the controller module.
The two-axis beam steering mechanism has two reflective optical elements, each mounted on its own coupling shaft. Each of the optical element coupling shafts is connected to the output of separate galvanometer servomotors. The two galvanometer servomotors are mounted in such a way as to provide a three-dimensional beam output profile. The beam profile that is produced is in the shape of an inverted pyramid with concave sides that expands at the base as the distance from the imaging system increases.
The photo optic feedback component includes a photo optic sensor, a band pass light filter and an adjustable reflective element. The photo optic sensor and band pass filter are mounted orthogonal to the return light path of the laser beam. The adjustable reflective element is mounted so as to direct a portion of the return beam of laser light to the photo optic sensor. A timing device, which includes a high-speed chronometer, is coupled to the optic feedback system to provide a distance ranging system that allows for measuring the distance between the imaging system and a retro-reflective surface. The distance measurement is accomplished by measuring the time of flight of the laser light from the time that a pulse is emitted from the 3D imaging system to the time that the return pulse is received at the photo optic sensor.
The controller module is the brain of the image system. It contains a microprocessor that controls the operation of the imaging system in response to various parameter inputs to properly project a 3D image onto a work piece. Typically, the controller module is a single-board computer that processes specific software commands.
The data storage device, which is coupled to the controller module, may contain the operating system platform software, the administrator application software, the operator application software, the laser database, the laser parameter sets database, a template image tool database, a parts database, and a jobs database. In a single head, stand-alone unit all of the software may reside on the data storage device of the imaging system. For example, by coupling infrared data transfer electronics in a keyboard and an infrared receiver to the imaging system head, a complete stand-alone unit without hardwire connection between the keyboard and the imaging system is possible. Some of the software may also reside on a separate, stand-alone computer connected to the imaging system head.
It is also possible to network multiple imaging heads into a system that allows coverage of relatively large work pieces. The use of multiple imaging heads also allows for better aspect ratio of a 3D work piece, i.e. covers work piece contours more efficiently. In a multi-head system, the controller module on one of the heads is configured as the master and the remaining heads are configured as slaves. Each head is connected to a hub using 10-base T Ethernet connection. The hub is typically connected to a server. In a multi-head system, the administrator and operator application software may be stored on the server, on a workstation, or some combination of the server, workstation and imaging head.
The method used by the present invention is unlike prior art devices. Prior art devices required that the 3D reference sensors must be in a known relationship to the 3D data set to be projected. Further, at least four reference points, and preferably six reference points are required for practical application. This is so because estimates for the x-y-z variables of the projector position and the q-r-s variables of the angular orientation of the projector are used in a Taylor series expansion and a least squares analysis iterates to improve the solution. The present invention determines the distance between the projector and the sensors using its internal range finding system. The 3D reference sensors"" x-y-z positions are calculated. A computer algorithm uses the calculated x-y-z positions of the 3D reference sensors to calculate the projector position. Because the distance between the projector and the sensors can be accurately determined, only three reference sensors are required to accurately project the template data set onto a work piece.